In facilities of the thermal and nuclear power plants, a pressure reducing mechanism is employed in order to constantly keep a flow rate of the sample water constant when high-pressure sample water is taken from a given portion of a circulating system for a boiler water and led to a water quality analyzer.
Conventionally, there has been proposed a pressure reducing mechanism a pressure reducing constant of which is maintained to be fixed. The pressure reducing mechanism has such a disadvantage that an outlet flow rate is varied as an original pressure of sample water changes.
In order to vary automatically the pressure reducing constant in response to a change of the original pressure of the sample water, there has also been proposed, as seen in FIG. 5, another flow control mechanism comprising a regulating lever 516 inserted into a pressure reducing mechanism 514, a fluid control cylinder 518 constituted by connecting one end of the regulating lever 516 to a spool 520, a flow control valve 522 for operating the fluid control cylinder 518, and a controller 528 for controlling the flow control valve 522 on the basis of a signal for contact operation generated by a pressure detector 526, as disclosed in Japanese Patent Publication No. 56-12806.
However, this type of the automatic pressure reducing mechanism has many structural problems such as a control delay due to a fluid pressure control, a low accuracy of positioning and a fluctuation in the pressure reducing constant due to leakage at a gland point of the adjusting lever and the like.
From the above viewpoint, there has also been proposed, as seen in FIG. 6, a pressure reducing mechanism 610 for sampling equipment, comprising two tubules 614 and 616 for effecting pressure control, each of which is provided on one end thereof with a fitting connected to a sample water line 612 and on the other end with a fitting 618 connected to a pressure control line 620, core rods 636 and 638, moving back and forth in the tubules 614 and 616, respectively, by drive means 634 for a feed screw 622 inserted into the pressure control line 620. A handle 646 can be manipulated to adjust the position of the feed screw 622 from outside the pressure reducing mechanism 610, as disclosed in Japanese Utility Model Publication No. 56-12592.
In such a pressure reducing mechanism, as well as conventional control mechanisms being used in general, when controlling the core rod inserted into the pressure control tubule by means of the feed screw, an automatic operation for controlling it at a high speed and with a high accuracy can not be realized even though no structural problems such as the fluctuation in the pressure reducing constant due to the leakage, etc. is caused.
The present inventors have developed an automatic pressure reducing equipment which is disclosed in Japanese Laid-Open Patent Publ. No. 57-100336. In that equipment, a pressure reducing mechanism (10) comprises inlet and outlet pressure control tubules (20, 24) into each of which is inserted a core rod (26, 28) supported by a movable ring (30). Into the movable ring (30) is screwed a threaded shaft (32) which is movably supported in the pressure reducing line. The pressure reducing mechanism (10) is connected to a sample water line (22) so as to detect a sample water pressure on the outlet side and keep the outlet pressure equal to the present one by adjusting the threaded shaft (32). Also, the pressure reducing mechanism (10) is provided on the outlet-side sample water line (22) with a pressure transducer (64) for generating a pressure signal and with a proportional controller (70) for transmitting an operation signal to a servo motor (36) after comparing the pressure signal with the preset pressure. A gear (40) is provided on a revolving shaft (42) derived through a reducer (38) from the servo motor (36) in order to engage another gear (52) provided on one end of the threaded shaft (32). Furthermore, a potentiometer (58) for detecting the number of revolutions of the servo motor (36) is provided so as to indicate an insertion of the core rods (26, 28) (see FIGS. 7 to 9).
Since, in the above-mentioned conventional pressure reducing mechanism which used two tubules for pressure control and the core rods being movable back and forth in the tubules, there is only extremely narrow clearance therebetween, the sample water may be prevented from passing through the clearance or a movement of the core rods in the tubules may be interrupted due to an accumulation of impurities contained in the sample water and an entrance of sludge into the clearance and the like. On the other hand, the core rods are fixedly connected to a common movable member in the pressure control line. The movable member is provided with a threaded hole so as to fit the feed screw thereinto. The core rods can be moved together with the movable member by rotating the feed screw from the outside of the tubule. Accordingly, in case the core rods are stopped from moving back and forth in the tubule due to the reasons hereinbefore described, the movable member can not move in the axial direction of the threaded shaft. As a result, the movable member is forced to rotate together with the feed screw so that a pair of parallel core rods may be warped to be broken or become useless, whereby the pressure control tubules may be damaged. Further, in this pressure reducing equipment, a position of the core rod is detected on the basis of the number of revolutions of the feed screw because rotary drive is converted into reciprocating motion. Therefore, in order that the core rods are more accurately positioned in the pressure control tubules, a conversion coefficient must be strictly determined. However, some errors can be inevitably generated due to instrumental error, etc. so that a high precision positioning of the core rods can not be easily performed. Furthermore, in a conventional pressure reducing equipment, the pressure control tubules, a pressure control line and core rods are always designed with a constant relation therebetween and manufactured integratedly. Accordingly, even if any part of these components are broken or damaged, all of them must be replaced. Also, in case of changing a control range of a pressure reducing condition, the respective control ranges of all components must be changed. Thus, an amount of cost for a maintenance and a design change is extremely increased. Moreover, upon replacing operation of such a pressure reducing equipment, a line system for the sample water with a high pressure must be stopped to separate the pressure reducing equipment therefrom so that a great deal of time and labor is required for the replacement.
The applicants of the invention have now developed a pressure reducing mechanism for the automatic pressure reducing equipment which can realize a convenient maintenance and an improved control performance, and then filed a Japanese patent application regarding the pressure-reducing control mechanism. The pressure reducing control mechanism comprises the pressure control tubules, the core rods and the pressure control pipe members which can be separated from each other. The adjustment of a position of the core rods is effected together with detection of the position by using a linear control means for making rectilinear motion. Therefore, it is possible to facilitate a manufacturing process of the pressure reducing equipment and enhance the precise positioning of the core rods to effect a strict pressure reducing control.
Namely, the pressure reducing control mechanism for the automatic pressure reducing equipment comprising the first pressure control pipe member having a pair of pressure control tubules parallel to each other, on one end of each of which a connector communicating with the pressure control tubule is provided in order to be connected to an external line and from the other end of each of which the core rod being movable back and forth is inserted into the pressure control tubule, the second pressure control pipe member fluid-tightly connected to the other end of the first pressure control pipe member through a fixture, in which a slide lever is insertedly arranged such that one end of the slide lever is provided with a connecting member disconnectably attached to the core rods and the other end is sealed with a gland packing, and a control means for adjusting the positioning of the core rods in the pressure control tubules through the slide lever by motor-driving and reciprocating a rack lever, the rack lever being arranged parallel to the slide lever and connected on its one end through a connecting member to a tip portion of the slide lever.
However, in a conventional automatic pressure reducing equipment the automatic pressure reducing control is required to keep a constant pressure and flow rate suitable for feeding the sample water to an analysis system despite of a fluctuation in the original pressure of the sample water. For this reason, the conventional equipment employs an automatic pressure-reducing control system shown in FIG. 4. As shown in FIG. 4, reference numerals 10 and 12 represent the pressure reducing mechanism and an automatic pressure-reducing control unit for controlling the pressure reducing mechanism, respectively. The pressure reducing mechanism 10 is provided with an inlet 14a for feeding the sample water and an outlet 14b for discharging the sample water. The inlet 14a and outlet 14b are connected to an inlet line 16 for feeding the high pressure sample water to the pressure reducing mechanism and an outlet line 18 for discharging the pressure-reduced sample water therefrom, respectively. The inlet line 16 is provided with an inlet control valve 20 which is opened or closed by manually entering an open/close command signal while being automatically opened or closed under a constant pressure condition. The outlet line 18 is provided with a flow control valve 22 formed as a needle valve so as to communicate with the analysis system for the sample water. A relief valve 24 and a pressure detector 26 are connected to the outlet line 18 on the upstream side of the flow control valve 22. A pressure of the sample water is detected by the pressure detector 26. A signal of the detected pressure is transferred to a controller 28 which compares a preset value of the pressure with the detected value thereof to calculate a deviation between the two values. In order to perform a pressure control according to the calculated deviation, the controller 28 transmits to the automatic pressure-reducing control unit 12 a control command for adjusting a position of the core rods in the pressure reducing mechanism 10.
In case that such a conventional flow control system for the pressure reducing sample water is operated by a command of an automatic mode and the high pressure sample water within a permissible range of pressure is fed to the inlet line 16, the automatic pressure-reducing control unit 12 can perform an appropriate pressure-reducing feedback control through the controller 28. However, for example, if a pressure of the high pressure sample water is reduced below the permissible range and then the pressure reducing mechanism 10 is led to the minimum pressure-reducing (a pressure reducing value 0), the flow control valve 22 comprising the needle valve is rendered closed due to a shortage of the pressure of the sample water on the outlet line 18 so that the sample water is stopped to be fed to the analysis system. On the other hand, when the pressure of the sample water to be fed to the inlet line 16 is lowered, the inlet control valve 20 is automatically closed. In this case, even if the inlet control valve 20 is manually opened, the flow control valve 22 remains closed as long as the pressure of the sample water continues to be lowered.
Thus, when the original pressure of the high pressure sample water is lowered due to any causes, a continuous analysis of the sample water is essential to solution to the causes, particularly to a safety operation of thermal/nuclear power plants. Therefore, as described hereinbefore, it is required to improve the pressure reducing mechanism of the automatic pressure reducing equipment such that the pressure-reduced sample water can be fed to the analysis system even if the original pressure of the sample water is extremely lowered to eliminate a pressure reducing function of the pressure reducing mechanism.